Gear shaving



May 31, 1960 Original Filed Jan. 18, 1954 F. BOHLE EI'AL 2,938,436

GEAR SHAVING 3 Sheets-Sheet 1 INVENTORS.

May 31, 1960 F. BOHLE ETAL 2,938,436

GEAR SHAVING Original Filed Jan. 18, 1954 3 Sheets-Sheet 2 GEAR SHAVING3 Sheets-Sheet 3 Original Filed Jan. 18, 1954 WNW w\\ J M w /M w j W M aa a Q w. @w M MNHM M v Huh lllll i L 14L B Mm N R Q A Unite GEAR SHAVING111., assignors to Illinois Tool Works, Chicago, 111., a corporation ofIllinois I Sttes Patent Original application Jan. 18, 1954, Ser. No.404,657,

now Patent No. 2,780,146, dated Feb. 5, 1957. Divided and thisapplication Nov. 8, 1956, Ser. No. 621,068

5 Claims. (Cl. 901.6)

This invention relates to a gear shaving tool and a machine for shavinggears by means of it.

This application comprises a division of copending application, SerialNo. 404,657, filed January 18, 1954, and entitled Gear Shaving, PatentNo. 2,780,146, February 5, 1957.

Gear shaving is ordinarily practiced on a machine in g which the gear tobe shaved and the shaving tool are mounted on skew shafts, that is tosay, on shafts which are not parallel and do not intersect. The usualshaving tool has the form of a helical gear mating with the gear to beshaved. Transverse gashes providing cutting edges are formed in theteeth of the helical gear or tool, and the teeth of the tool are forcedinto the spaces between the teeth of the gear. One of the shafts ispower-driven and the other is floating. As a result, the cutter shavesroughnesses off the gear teeth but its cutting edges do not alwaysgenerate the surfaces desired on the gear teeth and, therefore, do notcorrect inaccuracies in these teeth which may have resulted from thehobbing operation by which the gear was made.

Accurate surfaces on gear teeth could be generated by a cutter havingthe general form of a helical gear if the "cutter were provided withcutting edges extending along the lines of travel of the points ofcontact between its teeth and the gear teeth. We have discovered that acutter in the form of a helical gear may be provided with such cuttingedges by cutting off one end of its teeth by an appropriate surface ofrevolution about the axis of the gear. A cutting tool made in this wayis easy to produce, and the sharpening of this tool is easy, as itrequires merely rotating the tool about its axis and grinding thesurface of revolution at the end of the teeth so as to sharpen all thecutting edges simultaneously with a single grinder.

In the new cutting tool made in this way, cutting edges of the desiredform appear only at one side of each to'oth of the tool. These cuttingedges are acute and are well adapted to scrape one side of each tooth ofa gear meshing with the tool, and in so doing to generate an accuratesurface on one side of the gear teeth when the cutting tool and the gearare turned in timed relation.

Largely because of its action upon only one side of the gear teeth, theacute edges of the new scraper or shaving tool tend to urge the gear toturn in the direction in which it is being rotated by its shaft in theshaving operation. Since the pressure of the shaving edges on theunfinished gear teeth is necessarily irregular, the shaving operation isnot satisfactory unless carried out in a machinewhich prevents irregularforward movement of the gear under the influence of thescraper or tool.

In accordance with the invention, such movement of the gear is preventedby applying the driving power directly to the shaft on which the gear ismounted and indirectly to the cutter shaft through the timing gearingconnecting the two shafts. This results in making the stress on theconnecting gearing caused by engagement between the cutting edges of thetool and the teeth of the ice gear in the same direction as the stresson this gearing caused by the power drive, so that the gears of thegearing are constantly held in driving contact and prevent irregularforward movement of the gear.

Accordingly, a gear shaving machine embodying the invention, whereby animproved method of shaving may be practiced, comprises a cutting tool inthe form of a helical gear in which one end of the threads is'cut by asurface of revolution, skew shafts for the tool and the gear to beshaved, timing gearing connecting the two shafts, and means for applyingdriving power directly to the shaft on which the gear is mounted.

The principal object of the invention is to provide a method of shavinginvolute gear teeth which will smooth the surfaces of involute gearteeth and at the same time generate accurate involute surfaces on theteeth, correcting any errors in hobbing.

Other objects and advantages will become apparent from the followingdescription and the accompanying drawings, wherein:

Fig. 1 is an elevational view of a novel shaving tool contemplated bythe present invention;

Fig. 2 is a fragmentary sectional view of the shaving tool takensubstantially along the line 22 of Fig. 1;

Fig. 3 represents the system of coordinates which ex} presses theforrnula for the hyperbola defining the surface of revolution containingthe shaving edge .of the tool;

Fig. 4 is an elevational view disclosing a rotary shaving tool structurecomprising a pair of cutter members mounted upon the same cuttersupporting arbor;

Fig. 5 is a side elevational view of gear teeth shaving apparatusembodying the principles and structural features of the presentinvention;

Fig. 6 is an end elevational view of the apparatus shown in Fig. 5 andtaken along line -6-6 of Fig. 5; and,

Fig. 7 is a horizontal cross-sectional view taken substantially alongline 77 of Fig. 6.

Itis well-known that when two involute gears operate on skew axes, oneor both of the gears being of the spiral type with helicoidal teeth, theteeth of the two gears have a point contact; and, as the gears rotate,the contact point moves along a straight line called the path of contactwhich is fixed in space in a skew position relative to the axis of eachgear. In spite of general knowledge of these facts, it appears notbefore to have been recognized that the line of travel of the point ofcontact on one of the gears may be determined by finding theintersection of the side surfaces of its teeth withthe surface ofrevolution generated by the relative movement of the line of contact andthe gear. Since 'the path of contact is in a skew position with respectto the gear axis, the surfaceof revolution which it will generate withrespect to this gear is a hyperboloid of revolution. The formula for thehyperbola defining this surface can be expressed in the system ofcoordinates shown in Fig. '3. The x axis is positioned along the axis ofthe gear and the y axis is in the transverse plane containing the pointat which the path of contact is tangent to the base cylinder of the'gear. In these coordinates, the formula for the hyperbola is:

x=tan a ;y r

where a is the base helix angle of the gear as defined in conventionalinvolute gear geometry, and r is the base radius of the gear. V

Fig. 1 is a side elevational view of a shaving tool designated generallyby the numeral 1, which comprises a plurality of helical involute teeth2, the left extremities of which have been cut away so as to providehyperbolic surfaces 3. By cutting away or relieving in this manner oneextremity of each of the teeth 2, shaving edges 4 are presented. Theseshaving or cutting edges 4 will pass through every point of contact withthe flanks of the teeth of a complementary gear member.

As previously pointed out, the line of travel of the point of contactmay be determined by finding the intersection of the side surfaces ofthe teeth 2 with the surface of revolution 3 generated by the relativemovement of the line of contact and a complementary gear. In Fig. 3 thestraight line 5 is a projection of the path of contact. This path of thepoints of contact remains fixed as the shaving cutter rotates, andtherefore sweeps out a surface of revolution which in the presentinstance is a hyperboloid of revolution as defined by the surface 3. Theshaving or cutting edges 4 formed by the intersection of the hyperboloidwith the 'involute helicoidal tooth form have the desired property ofpassing through every point of the path of contact because thehyperboloid is the locus of all positions the contact can have relativeto complementary gear teeth. In Fig. 3 the hyperboloid is indicated bythe line 6, and the pitch point, namely the point at which the line 5 istangent to the line 6, is indicated by the numeral 7. It should also beunderstood that each hyperboloidal surface 3 is at right angles to theadjacent tooth flank at every point along the cutting edge 4. However,the cutting edge 4, when considered in a transverse section taken normalto the cutter axis, is acute and therefore facilitates the shaving orscraping action of the edge 4 upon the flank of a complementary geartooth.

In order for a clear understanding of the functioning of a shaving toolas contemplated by the present invention, it will now be described as apart of a shaving machine designated generally by the numeral 10, seeFigs. 5, 6 and 7. The machine 10 forms an attachment or fixture which isadapted to be mounted on any standard lathe or the like having avariable speed power drive 12, a driving shaft 14, a pair of spacedguideways or tracks 16 and 18, and a feed screw 20.

The fixture 10 includes a base or carriage plate 22 having slides 24 and26 bolted or otherwise secured thereto and slidably mounted upon thetracks 16 and 18. A plate member 28 depends from the carriage plate 22for rotatably mounting a hand wheel 30, which wheel is interconnected byany conventional means, not shown, with the feed screw so that uponrotation of the wheel, the carriage is traversed along the tracks 16 and18.

A housing 32 is rigidly mounted on the carriage plate 22 for supportingand enclosing work and cutter mounting arbors or mandrels and suitablegearing transmission therefor. As shown best in Fig. 7, a mandrel 34 forsupporting a work piece, such as gear 36, is rotatably journaled inbearings 38 and 40 on the housing 32. The mandrel 34 is connected to thedrive shaft 14, Fig. 5, by a suitable coupling 42. The bearings 38 and40 support and maintain accuracy of alignment of the mandrel 34, and areslidable longitudinally of the mandrel 34 as an incident to the shiftingof the housing 32 along the guideways 16-18. This shifting of thehousing 32 enables the shaving tool 1 to be fed acrossthe periphery ofthe rotating work or gear member 36 in a manner about to be described.

The shaving tool 1 is mounted on an arbor 46 which is disposed at a skewangle to the axis of the work piece supporting mandrel 34. The arbor 46is journaled in the housing 32 by suitable bearings 48 and 50. Thebearing 48 includes an annular thrust receiving portion 52 which isadapted to cooperate with a thrust bearing member 54 mounted on thearbor. The arbor 46 is driven by means of a gear chain or change geartransmission which includes a helical gear 56 rigidly secured to theinner end of the arbor. The gear 56 cooperates with a thrust receivingportion 58 of the bearing 50, to secure the arbor 46 and associatedparts against longitudjnal displacement relative to the housing 32.

The gear train for driving the shaving tool supporting arbor 46 alsoincludes a helical pinion 60 keyed upon a shaft 62 and this pinionmeshes with and drives the gear 56. The shaft 62 is driven by a helicalgear 64 keyed thereto, which gear is in turn driven by a gear 66 keyedto a shaft 68. The shaft 68 has a bevel gear 70 fixed thereto, whichmeshes with and is driven by a complementary bevel gear 72 keyed to thework or gear driving mandrel 34. From the foregoing it will be apparentthat the gear member 36 has a backlash free coupling with the drivemandrel 34 and that the rotary shaving tool is driven through a geartransmission from said mandrel.

Referring now to Fig. 7, it will be seen that the bevel gear 72 ismounted on the mandrel 34 for sliding movement longitudinally of themandrel by means of a key 74 secured to the mandrel by screws 76. Thekey 74 thus provides a driving connection between the mandrel 34 and thegear 72 while permitting the gear to move longitudinally of the mandrelalong with the housing 32 during a feeding movement of the shavingtool 1. The gear 72 is retained against longitudinal movement relativeto the housing 32 by means of a bearing member 78 fixed to the housingby screws 80 and having an inwardly extending annular thrust bearingportion or flange 82 which projects into an annular groove 84 in thebody of the gear.

The shaft 68 is journaled in suitable bearings 86 and 88 mounted in thehousing 32. The bearing 88 has an annular thrust receiving portion 90engageable with a shoulder 92 on the shaft 68 for preventinglongitudinal movement of the shaft in one direction. The shaft isrestrained against movement in the opposite direction by means of athrust plate 94 secured thereto by means of a screw 96.

It should be noted that the gear 36 is rigidly retained against rotationrelative to the mandrel 34 by a suitable locking key, not shown, and nutmeans 100, and the shaving tool 1 is likewise rigidly secured to thearbor 46 bya suitable key, not shown, and nut means 104. The rotary tool1 is synchronized with and driven at a predetermined speed ratio withrespect to the speed of rotation of the work or gear member 36.

As previously set forth, each cutting edge 4 conforms generally to apath of point contact which the advancing side of each tooth element 2will make with the finished gear 36. This arrangement of the shaving orcutting edges insures good cutting action, permitting relatively highspeed, accurate shaving. In addition, this arrangement of the shavingedges enables the mandrel 34 and the arbor 46 to be disposed at arelatively large skew angle so that the sliding action between the tooland the work or gear member is increased. Preferably, the angle betweenthe axes of the tool and the work is between 15 and 60 in order toobtain the desired shaving speeds.

As set forth above, the gear member 36 and the shaving tool 1 are bothpositively driven in synchronism with each other. It is common toprepare gear teeth for sub.- sequent shaving or finishing by a roughinghobbing process. This consists in roughing out the teeth in the gearblank so that the teeth will be sufficiently oversize to permitsubsequent finishing or shaving thereof. Inaccuracies or repetitiveerrors in the roughing hob such, for example, as errors in helicalalignment of the hob teeth, may result in corresponding inaccuracies inthe roughed out gear teeth. It is very important that such inaccuraciesbe eliminated in the complcted gear. To accomplish this, the presentinvention contemplates the elimination of backlash in the gear and tooldriving mechanism. By employing a backlash free coupling between therotary gear support and the source of rotary power supply, such as thedriving mandrel or shaft 34, an by coup ing this drive shaft 34 with hesha ing utis accomplished by the structure shown in Fig. '7.

ter 1 through the gear transmission as disclosed, the teeth 2 andshaving edges 4 of the tool coact with the complementary flanks of theteeth in the gear 36 so as to generate desired smooth and accurate gearteeth contours. In other words, the direct coupling of the gear with thesource of rotary power, together with the cutting or shaving force ofthe edges 4 acting against the gear teeth as though these edges weredriving the gear, completely eliminates backlash which might otherwiseresult. In shaving processes heretofore employed when a shaving cutterwas driven against a freely rotatable gear member, errors resulting frombacklash difiiculties were experienced. By eliminating backlash as justdescribed, errors in the gear teeth which may have been introducedduring the previous forming or bobbing operation are corrected duringthe shaving operation.

To adjust the depth of the cut made by cutting edges 4 into the flanksof the gear teeth, it is merely necessary to rotate the tool 1 a slightamount relative to the gear member. Such rotative adjustment of the tool1 The shaft 62 carrying the helical gears 60 and 64 is not onlyrotatably supported by bearings 112 and 114, but is also axiallyadjustable in said bearings. An adjusting screw 116 is threaded into asuitable nut-like member 118 mounted on the housing 32, and the innerextremity of the shaft 62 bears against a ball-type thrust bearing 119.The shaft 62 is continuously biased against the adjusting screw 116 by acompression spring 121 disposed within a cup-shaped closure member 123secured to the housing. Preferably, the spring 121 acts upon the shaft62 through a ball-type thrust bearing 125. It will be apparent that uponrotation of the adjusting screw 116, the shaft 62 may be adjustedaxially in opposite directions. Upon such axial adjustment of the shaft62, the helical gears, 56, 60, 64 and 66 will experience slightrotation. Variation in the degree of rotation imparted to the tool inresponse to a given axial adjustment of the shaft 62 may be obtained byemploying change gears of different helix angles. In the disclosedembodiment the helix angle of the gear 56 is about while the helix angleof the gear 66 is about 25. By properly coordinating the helix angles ofthe gears 56 and 66 and the lead of the screw threads on the adjustingscrew 116, accurate, fine adjustments of the depth of the cut may beobtained.

The method of finishing gears with the above described apparatus is asfollows. The work or gear member 36 and the cutting tool 1 are securedto their respective mandrels, and the cutting tool 1 is adjusted bymeans of the thumb screw 116 to provide the desired depth of cut. Thepower source 12 is then energized so that the cutting tool and the workpiece are driven in the manner described above. The housing 32 carryingthe shaving tool is then fed axially of the mandrel 34 by means of thehand wheel 30. As the tool 1 moves across the work piece, one flank ofeach of the work piece teeth is accurately finished regardless of anyinaccuracies which may have been present in the initial rough formingoperation. The particular shape of the shaving edges 4 of the tool 1 andthe relatively large angular relationship be tween the axes of the tooland the gear member enable improved, high speed shaving action so thatthe tool may be fed relatively rapidly across the work periphery withoutdanger of producing undesirable scallops in the flanks on one side ofthe gear teeth. In order to finish the opposite flanks on the oppositeside of the gear teeth, the gear member is removed and then remounted onthe mandrel in reverse position, whereupon the above described operationis repeated. Thus shaving of one side of the teeth is performedindependently of the shaving of the opposite side.

The method of this invention can be carried out by a double shaving toolas illustrated at 176 and 178 in Fig. 4, wherein the two shaving members176 and 17.8 are mounted on an axially shiftable arbor. Upon rotation ofthe arbor in one direction, the shaving edges of the member 176 finishthe flanks on one side of the teeth of the gear 36. Subsequently, thearbor is shifted axially and rotated in the opposite direction, and theshaving edges of the member 178 finish the flanks on the opposite sideof the teeth. Since the shaving members 176 and 178 are axially spacedfrom each other, neither of them interferes with or engages the workwhen the other is being used. As will be understood, the shaving membersand the gear being finished are adjustable relatively toward and awayfrom each other transversely of their axes for finishing gears ofdifferent sizes.

Preferably the shaver or shavers are capable of selective positioning oneither side of the work, i.e. in front of the work as in Figs. 4 and 7,or behind the work. Such selective positioning allows for a choice ofhelix angles in the shaving members which is most suitable for a gearmember with helical teeth. It will be apparent that for any given gearthere is thus a choice of one of two possible helix angles for theshaving member, thereby affording the best cut or shaving action.

The shaving action according to the method described herein is at highspeeds. Therefore, the cutter or shaving tool preferably is of carbide,or is provided with carbide inserts, carbide inserts in general beingknown in the art. This is possible since the cutting or shaving tool isreadily ground on a form grinder.

It will be apparent from the foregoing description that the presentinvention contemplates a simple and improved method Whereby flanks ofteeth such as gear teeth, involute splines and the like, may be finishedor shaved with great accuracy and with increased speed. By drivingshaving edges of a rotating shaving tool against the flanks on one sideof the teeth of the rotatably supported gear member, and rotatablydriving the gear member in timed relation with the movement of theshaving edges and relatively shifting these edges and the gear teethaxially, predetermined smooth and accurate flank contours are generated.The flanks on the opposite sides of said gear teeth may be similarlygenerated by reversing the position of the work or tool on itsrespective support and applying the same shaving edges or by applying aseries of other shaving edges without the necessity of reversing theposition of the work or tool. Elimination of backlash diflicultiesrepresents another important contribution of the present invention. Theinvention also lends itself for shaving gear members of varying sizesand shapes and insures economy in the cost of shaving tool design andmaintenance.

Certain specific disclosures, both structural and schematic, have beendisclosed herein for the purpose of indicatingpractical embodiments ofthe invention, and it will be understood that other modifications andchanges may be made without departing from the spirit and scope of theappended claims.

We claim: a

1. The method of finishing the flanks of gear teeth and the like whichcomprises the steps of driving peripheral circularly aligned shavingedges of a rotating shaving tool against the flanks on one side of theteeth of a rotatably supported gear member in skew axis relationtherewith, said shaving edges lying along the lines of travel of thepoint of contact between the gear teeth and the teeth of a conjugategear, rotatably driving the gear member in timed relation with themovement of said shaving edges and relatively shifting said shavingedgesand gear teeth axially of the gear member so as to generatepredetermined flank contours, and driving peripheral circularly alignedrotating shaving edges similarly against the opposite flanks of saidgear teeth so as to generate complementary flank contours.

2. The method of finishing the flanks of gear teeth and the like whichcomprises the steps of driving peripheral circularly aligned shavingedges of a rotating shaving i091 against the flanks on one side of theteeth of a rotatably supported gear member in skew axis relationthereto, said shaving edges lying along the lines of travel of the pointof contact between the gear teeth and the teeth of a conjugate gear,rotatably driving the gear member in timed relation with the movement ofsaid shaving edges and relatively shifting said shaving edges and gearteeth axially of the gear member so as to generate predetermined flankcontours, and subsequently driving another series of peripheralcircularly aligned rotating shaving edges similarly against the oppositeflanks of said gear teeth so as to generate complementary flankcontours.

3. The method of finishing the flanks of gear teeth and the like whichcomprises the steps of driving peripheral circularly aligned shavingedges of a rotating shaving tool against the flanks on one side of theteeth of a rotatably supported gear member in skew axis relationthereto, said shaving edges lying along the lines of travel of the pointof contact between the gear teeth and the teeth of a conjugate gear,rotatably driving the gear member in timed relation with the movement ofsaid shaving edges and relatively shifting said shaving edges and gearteeth axially of the gear member so as to generate predetermined flankcontours, subsequently driving peripheral circularly aligned rotatingshaving edges similarly against the opposite flanks of said gear teethso as to generate complementary flank contours, and during the shavingoperation, maintaining the shaving tool free from contact with theflanks of the gear teeth opposite from those which are being shaved.

4. The method of finishing the flanks of gear teeth and the like whichcomprises the step of driving peripheral, circularly aligned shavingedges of a rotating shaving tool in one direction of rotation againstthe flanks on one side of the teeth of a rotatably supported gear memberin skew axis relation thereto while maintaining confronting circularlyaligned shaving edges out of contact with the gear member, rotatablydriving the gear member in timed relation with the movement of saidshaving edges and relatively shifting said shaving edges and gear teethaxially of thegear member so as to generate predetermined flankcontours, shifting axially of said shaving tool and reversely drivingall of said shaving edges whereby said confronting shaving edgesgenerate complementary flank contourson the opposite flanks'of the gearteeth while the first mentioned shaving edges are maintained out ofcontact with the gear teeth.

5. The method of finishing the flanks of gear teeth and the like whichcomprises the steps of driving peripheral circularly aligned shavingedges of a rotating shaving tool against the flanks on one side of theteeth of a rotatably supported gear member in skew axis relationtherewith, said shaving edges lying along the lines of travel of thepoint of contact between the gear teeth and the teeth of a conjugategear, rotatably driving the gear member directly and the shaving toolindirectly from the gear member, in timed relation and relativelyshifting said shaving edges and gear teeth axially of the gear member soas to generate predetermined flank contours, and subsequently drivingperipheral circularly aligned rotating shaving edges similarly againstthe opposite flanks of said gear teeth so as to generate complementaryflank contours.

References Cited in the file of this patent UNITED STATES PATENTS2,147,864 Thrun Feb. 21, 1939 2,214,225 Drummond Sept. 10, 19402,232,408 Shaw Feb. 18, 1941 2,236,256 Allard Mar. 25, 1941 2,499,167Sanborn Feb. 28, 1950 2,581,701 Praeg Ian..8, 1952 2,660,929 Praeg Dec.1, 1953 2,749,802 Carlsen June 12, 1956 FOREIGN PATENTS 668,067 'GermanyNov. 25, 1938

